The invention relates to a sealing element, particularly for shut-off and regulating valves. It comprises a disc-shaped, piston-shaped or spherical shut-off body. The shut-off body can comprise a metallic or nonmetallic material. This material can be, for example, a ceramic material, including aluminium oxide and the various silicon carbides SiC, Si.sub.2 C and silicon nitride Si.sub.3 N.sub.4.
On a working surface (sealing surface) of the shut-off body, a hard material layer containing carbon and silicon is applied by plasma CVD or plasma polymerization in a coating chamber. The hard material layer here comprises a bonding layer component applied to the working surface of the shut-off body and a subsequent covering layer (sliding layer) component. The bonding layer component has a first silicon content favouring adhesion to the working surface of the shut-off body, and the subsequent carbon-containing covering layer component has a second silicon content lower than that of the bonding layer component, or is silicon-free, to achieve low coefficients of sliding friction and static friction.
The deposition from the plasma is carried out by ion bombardment, e.g. by means of a glow discharge or by means of an additional ion gun. From a hydro-carbon-containing atmosphere a wear-resistant, carbon-containing layer having sufficiently low coefficients of sliding friction and static friction can be deposited in this way.
A sealing element of the above type and the associated plasma CVD coating process is known from DE-A 38 32 692.
According to this document, shut-off bodies are, to coat their working surfaces, placed in the coating chamber on a specimen holder having a negative potential relative to the plasma. For initial physical etching of the working surfaces of the shut-off bodies with argon, the coating unit is first operated as cathode atomization (sputtering) unit. For subsequent deposition of the bonding layer component of the hard material layer on the etched working surface, the same unit is then operated under certain first process parameters as high-frequency plasma CVD unit, with the argon gas in the coating chamber being replaced, for example by tetramethylsilane. Under altered second process parameters, the covering or sliding layer component is then deposited from a gas mixture of tetramethylsilane and hexane after deposition of the bonding layer component.
The sealing elements obtained by this method (these can advantageously be coated ceramic plates for water valves, e.g. single-hand mixers) have, thanks to the hard material layer applied, sufficiently low coefficients of sliding friction and static friction when sliding over one another, even in the presence of water, so that greasing of the sealing surfaces as has hitherto been required for uncoated ceramic plates is no longer necessary.
A disadvantage of the known sealing plates is that their hot-water resistance is in many cases unsatisfactory. This is the case particularly when a hot-water resistance of more than 1000 operating hours is to be achieved without the hard material layer applied becoming detached from the shut-off body.